We plan to investigate in rabbits quantitative changes in the metabolism of both endogenous and exogenous sulfite which result from sulfite oxidase deficiences produced by dietary manipulation. Assessment of the metabolism of exogenous sulfite will be made using pharmacokinetic techniques. Changes in plasma S-sulfonate concentration and in cysteine S-sulfonate and thiosulfate excretion will be measured to determine which metabolite is the most sensitive indicator of decreased sulfite oxidase function. These experiments are closely related in purpose to a collaborative study with Dr. Holstein of the Mt. Sinai School of Medicine in which the feasibility of using plasma S-sulfonate concentration as an indicator of varying degrees of sulfite oxidase deficiency in humans is being investigated. This study will continue in the coming year. Other areas of investigation to be pursued include the initiation of experiments designed to determine the teratogenic potential of sulfite, and the separation and characterization of plasma proteins which are susceptible to sulfitolysis in vivo.